Valve pin with thermocouple

ABSTRACT

A valve pin for use in a melt channel in an injection molding machine. The valve pin has a valve pin body and at least one thermocouple substantially completely inside the valve pin body.

This is a reissue of Ser. No. 10/268,885 of U.S. Pat. No. 6,739,863 andclaims the benefit of U.S. Provisional Application No. 60/328,404 filedOct. 12, 2001.

FIELD OF THE INVENTION

This invention relates to an injection molding machine, and moreparticularly to a valve pin for a nozzle in an injection moldingmachine.

BACKGROUND OF THE INVENTION

It is well known that it is desirable to measure the temperature of themelt throughout the length of a nozzle on a hot runner injection moldingmachine, and at the gate into a mold cavity.

Several attempts at taking this measurement have been made. Typically, athermocouple is included on the nozzle and is mounted to the exterior ofthe nozzle body. In order to take measurements that better represent thecondition of the melt, the tip of the thermocouple is usually positionedwithin an aperture that penetrates into the nozzle body so that the tipof the thermocouple is positioned nearer to the nozzle melt channel. Theaccuracy of the thermocouple is hampered, however, by the proximity ofthe thermocouple to the nozzle heater, which is typically positioned onthe exterior of the nozzle. Thus, the proximity of the thermocouple tothe nozzle heater itself prevents the thermocouple from accuratelymeasuring the temperature of the melt.

Another example of an attempt to measure the melt temperature at thegate is disclosed in European Patent Application EP 99304442.9 (Goldwinet al.). Goldwin et al. discloses the use of a conductive film to coatthe outside of a valve pin that passes through the nozzle melt channel.The conductive film could be used to measure the temperature of the meltin the nozzle melt channel. However, the film is repeatedly exposed to acycling of pressures, and is constantly abraded by the melt flowingthrough the nozzle into the mold cavity.

Yet another example of an attempt to measure the melt temperature at thegate is disclosed in U.S. Pat. No. 5,334,008 (Gellert). Gellertdiscloses a thermocouple, having a sensing portion that is fixed insidea valve pin guiding element in a melt channel. The guiding elementdivides the melt flow, however, and creates an obstruction in the meltchannel. Furthermore, the thermocouple is fixed within the melt channel,and cannot therefore obtain temperatures from different positions withinthe melt channel.

For some applications, it may be advantageous to measure a plurality oftemperatures. For example, in some co-injection applications, wherethere are flows of more than one melts into a mold cavity, it may bedesirable to measure the temperatures of some of the melts individually,and/or some of the melts after they have combined. In order to achievethis using fixed thermocouples of the prior art, a plurality ofthermocouples may be needed to be incorporated into the co-injectionnozzle. In the event that one of the thermocouples fails for any reason,it can be relatively difficult to access the failed thermocouple toreplace it.

Thus a need exists for new devices for the measuring of the temperatureof the melt at the gate into a mold cavity in a hot runner injectionmolding machine.

SUMMARY OF THE INVENTION

In a first aspect, the present invention is directed to a valve pin foruse in a melt channel in an injection molding machine, including a valvepin body and at least one thermocouple positioned substantiallycompletely inside the valve pin body for measuring the temperature ofmelt in the melt channel.

In a second aspect, the present invention is directed to a nozzle for aninjection molding machine, incorporating the valve pin described above.

In a third aspect, the present invention is directed to a method ofmaking a valve pin for use in a melt channel in an injection moldingmachine, the method comprising:

-   -   providing a valve pin body having a chamber therein;    -   inserting thermocouple substantially completely into the        chamber; and    -   at least partially filling the chamber with a retainer to retain        the thermocouple therein.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show moreclearly how it may be carried into effect, reference will now be made byway of example to the accompanying drawings, in which:

FIG. 1 is a sectional view of a portion of an injection molding machine,which has a nozzle and a valve pin in accordance with a first embodimentof the present invention, the valve pin being in the open position;

FIG. 2 is a sectional view of the portion of the injection moldingmachine shown in FIG. 1 with the valve pin in the closed position;

FIGS. 3a, 3b and 3c are sectional views showing the construction of thevalve pin shown in FIG. 1;

FIG. 3d is a side view of a valve pin in accordance a second embodimentof the present invention;

FIG. 4 is a sectional view of the portion of an injection moldingmachine including the valve pin shown in FIG. 1 and another nozzle;

FIG. 5 is a sectional view of the portion of an injection moldingmachine including the valve pin shown in FIG. 1 and yet another nozzle;

FIG. 6 is a sectional view of the portion of an injection moldingmachine including the valve pin shown in FIG. 1 and yet another nozzle;

FIG. 7 is a sectional view of the portion of a multigate injectionmolding machine including the nozzle and the valve pin shown in FIG. 1;

FIGS. 8a, 8b, and 8c are sectional views of a portion of a co-injectioninjection molding machine including the valve pin shown in FIG. 1 andyet another nozzle; and

FIG. 9 is a sectional view of a valve pin in accordance with a thirdembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made to FIGS. 1 and 2, which show an injection moldingmachine 10 having a valve pin 11 in accordance with a first embodimentof the present invention. Injection molding machine 10 includes amanifold block 12, a plurality of nozzles 14 and a mold cavity block 16.The manifold block 12 may have many possible melt channelconfigurations. For example, as shown in FIG. 1, the manifold block 12may include an inlet 18, and a plurality of melt channels 19, includingan inlet melt channel 20, a plurality of intermediate melt channels 22downstream from the inlet melt channel 20 and a plurality of outgoingmelt channels 24 downstream from the intermediate melt channels 22. Themanifold block 12 is heated by a heater 26. Heater 26 may be anysuitable type of manifold heater known in the art.

The nozzles 14 are positioned downstream from the outgoing melt channels24. Each nozzle 14 includes a nozzle body 28, which has a nozzle meltchannel 30 therein. The nozzle 14 is heated by a nozzle heater 32, whichmay be mounted to the nozzle 14 in any way known in the art. Forexample, nozzle heater 32 may surround the exterior of the nozzle body28, as shown in FIG. 1, or alternatively, nozzle heater 32 may beembedded within nozzle body 28. The nozzle melt channel 30 ends at agate 34, which is the entrance from the nozzle melt channel 30 into amold cavity 36 in the mold cavity block 16. Mold cavity block 16 may becooled by a cooling fluid in cooling channels 37.

Melt passes from a melt source (not shown), through inlet 18 in manifoldblock 12, through melt channels 20, 22 and 24, through the nozzle meltchannels 30 and through gates 34 into mold cavities 36.

Valve pins 11 are positioned within the nozzle melt channels 30 tocontrol the flow of melt into the mold cavities 36. Valve pins 11 may bemovable within the nozzle melt channel 30, as shown, by an actuator 38.Alternatively, valve pins 11 may be stationary within nozzle meltchannel 30.

Actuator 38 may be any suitable type of actuator. For example, actuator38 may include a chamber 40, having a first fluid passage 42 proximateone end of the chamber 40, a second fluid passage 44 proximate theopposing end of the chamber 40, a piston 46 in the chamber 40 and a arm48 extending from the piston 46 to outside the chamber 40. The arm 48may connect the piston 46 inside the chamber 40 to the valve pin 11,using any suitable connection means. For several reasons including easeof cleanout, the arm 48 preferably connects to the valve pin 11 outsideof any melt channels 19 and 30, so that the melt is not permitted toseep into the connection. The arm 48 itself may be fixedly connected tothe piston 46.

A fluid, such as, for example, hydraulic oil or air, may be introducedinto the chamber 40 on one side of the piston 46 at a selected pressureand/or removed on the opposing side of the piston 46 to move the piston46, (and in turn, the arm 48 and the valve pin 11), in a directioneither towards or away from the gate 34. The movement of the valve pin11 towards and away from the gate 34 may be, for example, to control themelt flow into the mold cavity 36.

The valve pin 11 passes from outside the outgoing melt channel 24 intothe outgoing melt channel 24 through a mold plug 50. Mold plug 50 sealsaround valve pin 11 to inhibit melt from escaping from outgoing meltchannel 24. The mold plug 50 may further permit sliding of the valve pin11 therethrough, so that valve pin 11 can move, as desired in meltchannels 24 and/or 30. In the position shown in FIG. 1, valve pin 11 isin the open position, that is, the position in which melt flow ispermitted into mold cavity 36.

Valve pin 11 includes a valve pin body 52, which has an end 54. The end54 may be tapered, as shown in FIGS. 1 and 2, or alternatively, may haveany suitable shape, such as cylindrical. The end 54 may be used forgating purposes, ie. for the closing of the gate 34. In the positionshown in FIG. 2, the valve pin 11 is in the closed position, with theend 54 being positioned in the gate 34, to prevent melt flow into moldcavity 36.

Valve pin 11 may further include a head 55. The head 55 may be used tofacilitate connecting the valve pin 11 to the piston 46. The head 55 maybe positioned at the end of the valve pin 11 opposed to the end 54. Thehead 55 may be a disc-shaped portion that has a larger diameter thanthat of the valve pin body 52. The head 55 may be captured by anysuitable means known in the art, so that the valve pin 11 is removablefrom the arm 48.

Valve pin 11 further includes a thermocouple 56. The thermocouple 56 maybe a two-wire type. For example, the thermocouple 56 may include a firstelectrical conduit 58, which may be a wire 58, a second electricalconduit 60, which may be a wire 60, and a sensing piece 62, whichconnects the wires 58 and 60 at one end. The wires 58 and 60 arepreferably insulated along their length, to inhibit being heated bysomething other than the sensing piece 62. The thermocouple 56 may be ofa configuration described in U.S. Pat. No. 5,009,718 (Schmidt), which isincorporated herein by reference.

Thermocouple 56 may be embedded in valve pin body 52, as shown, or mayalternatively, may extend in an internal passage in valve pin body 52.

The sensing piece 62 may be positioned proximate the end 54 of the valvepin body 52 to record the temperature of melt that is relatively closeto the gate 34. The term ‘proximate’ as used herein, indicates that thesensing piece 62 may be near end 54 or may be in the end 54.

The wires 58 and 60 from thermocouple 56 may exit from the valve pinbody 52 outside of the nozzle melt channel 30 and manifold outgoing meltchannel 24. Thermocouple 56 exits from valve pin 11 at an exit point 64.Exit point 64 may be at any suitable position on valve pin 11, such as,for example, on the side of the valve pin body 52, as shown. Theposition of exit point 64 should be such that the exiting wires 58 and60 do not interfere with the movement of valve pin 11 in melt channels24 and 30. Thermocouple 56 may be connected to a receiving device 65 forreceiving, processing, transmitting and/or recording the measurementsfrom thermocouple 56. Wires 58 and 60 should be long enough betweenvalve pin 11 and receiving device 65, so that they do not interfere withthe movement of valve pin 11.

By positioning the thermocouple 56 inside the valve pin body 52, thethermocouple 56 can measure the temperature of the melt while it isprotected from wear from the melt flow in the nozzle melt channel 30.This is in contrast to valve pins having a film-type thermocoupleapplied thereto where substantially all of the film-type thermocouple isexposed to the melt flow.

Reference is made to FIGS. 3a, 3b and 3c, which illustrate a method inaccordance with the present invention, for making valve pin 11.Reference is made to FIG. 3a. To make a valve pin 11 having athermocouple 56, a passage 66 may be made in valve pin body 52. Passage66 may be cast directly into the valve pin body 52, or may be machinedinto valve pin body 52. Passage 66 may be blind and may therefore endinternally in valve pin body 52 at any suitable point, such as, forexample, proximate to end 54, as shown in FIG. 3a. Aperture 68 is theopening of passage 66 to the exterior of the valve pin 11. Aperture 68may be positioned at any suitable point on valve pin 11. Aperture 68 mayact as the exit point 64 for the wires 58 and 60 from the valve pin body52.

Referring to FIG. 3b, the thermocouple 56 may be fed into passage 66 sothat the sensing piece 62 is positioned at the blind end of passage 66.Referring to FIG. 3c, the passage 66 may be filled fully or partiallywith a retainer 70, to hold the thermocouple 56 in place in passage 66.The retainer 70 may be thermally conductive, so that it increases thethermal conductivity between the sensing piece 72 and the melt flowsurrounding the valve pin 11, relative to an air gap that wouldotherwise surround the thermocouple 56 in the passage 66. The increasedthermal conductivity increases the accuracy of the thermocouple 56 inreading the temperature of the melt flow around the valve pin 11. Afterfilling the passage 66 with the retainer 70, the retainer 70 may besolidified as necessary to prevent the thermocouple 56 from beinginadvertently moved in the valve pin 11 during use.

Reference is made to FIG. 3d. As an alternative, valve pin body 52 mayinclude a passage 72, which passes through end 54 of valve pin 11, sothat there is an aperture 74 on the end 54 of valve pin 11. In thisalternative, the thermocouple 56 may pass through the aperture 74, sothat the sensing piece 62 of thermocouple 56 is flush with the surfaceof the valve pin at end 54. A suitable material may then be used to fillany air gap between the sensing piece 62 in the aperture 74, so that theend 54 of the valve pin 11 has a smooth surface.

Reference is made to FIG. 4, which shows valve pin 11 in use with anozzle 100. Nozzle 100 is similar to nozzle 14, except that nozzle 100may have a nozzle body 102 with an offset nozzle melt channel 104. Valvepin 11 may pass through manifold 12, through nozzle body 102 and intonozzle melt channel 104. Valve pin 11 may be actuated by actuator 38 ormay alternatively be stationary within nozzle melt channel 104.

Reference is made to FIG. 5, which shows a valve pin 11 in use with anozzle 110. Nozzle 110 is similar to nozzle 14, except that nozzle 110includes an actuator 112, which replaces actuator 38. Actuator 112 is arack-and-pinion type actuator, and includes a rack 114, a plurality ofpinions 116, and a plurality of valve pin holders 118. The rack 114 maymove laterally relative to the nozzles 110, along the line of directionshown by arrows A, and engages the pinions 116, which are mounted ontothe valve pin holders 118. The pinions 116 and the valve pin holders 118rotate in response to the lateral movement of the rack 114. The valvepin 11 in this case, rotates to control the flow of melt to the gate 34,rather than moving towards and away from the gate 34. A rack-and-pinionactuator construction that may be used with the valve pin 11 having thethermocouple 56 therein, is described further in U.S. Pat. No 4,330,258(Gellert), which is hereby incorporated by reference. It isalternatively possible for a separate rack to be provided for eachpinion. As a further alternative, it is possible for the rack or racksto be positioned other than laterally.

Reference is made to FIG. 6, which shows a nozzle 150 with the valve pin11 in accordance with the present invention. Nozzle 150 is similar tonozzle 14, except that nozzle 150 includes a body 152 having a secondthermocouple 154 connected thereto. Thermocouple 154 may be used tomeasure the temperature of some portion of the nozzle 150 itself. Forexample, the thermocouple 154 may be used to measure the temperature ofthe nozzle body 152 or the temperature of the nozzle heater 32.

Reference is made to FIG. 7, which shows a multi-gate injection moldingmachine 200. Molding machine 200 may include a mold cavity plate 202with a plurality of mold cavities 204. Each mold cavity 204 may have aplurality of gates 206 permitting entry of melt into mold cavity 204from a plurality of points. Molding machine 200 may further includemanifold 12, and a plurality of nozzles 14, whereby more than one nozzle14 may feed melt to a single mold cavity 204. Valve pins 11 may beincluded in molding machine 200, to provide melt temperature informationfrom each nozzle 14 leading to a mold cavity 204.

Reference is made to FIGS. 8a, 8b and 8c, which show a co-injectionmolding machine 300 with a co-injection nozzle 302. Co-injection is theinjection of different materials into a single mold cavity 303 to form,for example, a product having several layers. Some of the layers may bemade from the same material, and some layers may be made from adifferent material. Some layers may flow into the mold cavity 303simultaneously, while some layers may flow into the mold cavity 303sequentially. Co-injection is used for many applications, such aspreforms for soft drink bottles.

Molding machine 300 may include a plurality of manifolds, such asmanifolds 304 and 306. Manifolds 304 and 306 receive melt from aplurality of melt sources (not shown), and may have a plurality of meltchannels therein, which are shown at 308, 310 and 312. Each melt channel308, 310 and 312 carries melt which forms a different layer of the finalmolded product.

Co-injection nozzle 302 may include a first nozzle melt channel 314, asecond nozzle melt channel 316 and a third nozzle melt channel 318,which receive melt from manifold melt channels 308, 310 and 312respectively. Such a configuration is described in PCT publication no.WO00/54954 (Gellert et al.). Nozzle melt channel 314 may be central andcoherent along its length, while melt channel 316 may be annular and mayjoin with melt channel 314, so that a second layer of material may beintroduced into melt channel 314. Melt channel 318 may also be annularand join melt channel 314 to introduce a third layer of material to meltchannel 314.

Valve pin 11 may be moved in melt channel 314 to permit the flow of thematerials into the melt channel 314 or to permit the flow of materialsinto the mold cavity 303. As valve pin 11 moves in melt channel 314,different temperature information may be obtained. For example, as thevalve pin 11 is in the closed position, shown in FIG. 8a, thermocouple56 may obtain temperature information on the melt in the mold cavity303, and particularly on the material in the gate area 320 of the moldcavity 303. Such temperature information can be useful, for example, tohelp control the rate of cooling of the mold cavity. It is advantageousto control the rate of cooling, to inhibit crystallinity development inthe molded part. As the valve pin 11 moves to the position shown in FIG.8b, the thermocouple 56 can obtain information on the melt flow fromnozzle melt channel 318. As the valve pin 11 moves to the position shownin FIG. 8c, the thermocouple 56 can obtain temperature information onthe melt in melt channel 314 received from melt channels 308 and 310.

Reference is made to FIG. 9, which shows a valve pin 400. Valve pin 400is similar to valve pin 11, except that valve pin 400 includes aplurality of thermocouples 56. Thermocouples 56 may be positioned atdifferent points within valve pin 400, so that temperature informationmay be obtained on different portions of a single melt flow, ordifferent melt flows.

Referring to FIG. 1, for example, the temperature of a nozzle, such asthe nozzle 14, typically varies over its length. Typically, the nozzle14 is hottest in the middle, and is cooler at the ends where it contactsthe manifold block 12 and the mold cavity plate 16 respectively, due totheir lower temperatures. Because of the temperature variation, it maybe useful to measure the temperature of melt at different points in thenozzle melt channel 30 simultaneously. By incorporating a plurality ofthermocouples 56 in the valve pin 400 (FIG. 9), the melt temperature canbe known simultaneously at a plurality of points along the length of thenozzle melt channel 30.

Referring to FIG. 9, a first thermocouple 402, and a second thermocouple404 may be provided in the valve pin 400. The first thermocouple 402 maybe positioned at or near the end of the valve pin 400, which is shown at406. The end 406 may be used for gating purposes, and may cooperate withthe 34 (FIG. 1) to seal against melt flow into the mold cavity 36 (FIG.1).

The second thermocouple 404 may be positioned spaced from the firstthermocouple 402, such as, for example, in a central portion 408 of thevalve pin 400. The central portion 408 is the portion of the valve pin400 that is adapted to be positioned generally in the region of thenozzle 14 (FIG. 1) the hotter central portion of the nozzle 14, which isspaced from its two ends, where the nozzle 14 contacts the mold cavityplate 16 and the manifold plate 12.

The actuator 38 has been described as being a hydraulic piston-type, andas a rack-and-pinion type. Alternatively, the actuator 38 may be anelectric rotary actuator, or an electric linear actuator, which can beconnected to the valve pin 11.

While the above description constitutes the preferred embodiments, itwill be appreciated that the present invention is susceptible tomodification and change without departing from the fair meaning of theaccompanying claims.

1. A valve pin for use in a melt channel in of an injection moldingmachine nozzle having a nozzle heater, comprising: a valve pin body; andat least one thermocouple positioned substantially completely insidecoupled to said valve pin body for measuring the temperature of melt insaid melt channel, wherein the temperature measurement is used incontrolling said nozzle heater.
 2. A valve pin as claimed in claim 1,wherein said at least one thermocouple includes a sensing portion and apair of electrical conduits for connecting said sensing portion to areceiving device.
 3. A valve pin as claimed in claim 2, wherein saidvalve pin body has an end that is adapted to be positioned proximate agate into a mold cavity, and said sensing portion of said at least onethermocouple is positioned in said end.
 4. A valve pin as claimed inclaim 3, wherein said sensing portion of said at least one thermocoupleis adapted to be exposed to melt when said valve pin body is positionedin said melt channel.
 5. A valve pin as claimed in claim 4, wherein saidsensing portion of said at least one thermocouple is flush with saidend.
 6. A valve pin as claimed in claim 2, wherein said valve pinincludes a first said thermocouple and a second said thermocouple, andsaid sensing portion of said first thermocouple is spaced from saidsensing portion of said second thermocouple.
 7. A valve pin as claimedin claim 6, wherein said valve pin body has an end that is adapted to bepositioned proximate a gate into a mold cavity, and said sensing portionof said first thermocouple is positioned proximate said end.
 8. A valvepin as claimed in claim 1 further comprising an actuator for moving saidvalve pin body in said melt channel.
 9. The valve pin as claimed inclaim 8, wherein said valve pin body is removably connected to saidactuator.
 10. A nozzle for an injection molding machine, comprising: anozzle body defining a nozzle melt channel therein, wherein said nozzlemelt channel is adapted to transfer melt from a melt source, to a gateinto a mold cavity; a heater connected to said nozzle body, wherein saidheater is located on said nozzle body for heating melt passing throughsaid nozzle melt channel; a valve pin positioned at least partially insaid nozzle melt channel, said valve pin including a valve pin body andat least one valve pin thermocouple positioned at least partially withinsaid valve pin body for measuring the temperature of the melt in saidnozzle melt channel, wherein the temperature measurement is used incontrolling said nozzle heater; and an actuator for moving said valvepin in said melt channel.
 11. A nozzle as claimed in claim 10, furthercomprising: a heater connected to said nozzle body, and wherein saidheater is located on said nozzle body for heating melt passing throughsaid nozzle melt channel; and a nozzle body thermocouple connected tosaid nozzle body.
 12. A nozzle as claimed in claim 10, wherein saidactuator includes a chamber and a piston that is movable within saidchamber, wherein said valve pin is connected to said piston, said pistonhas two faces, and said piston is adapted to be moved in said chamber bydifferential pressure of an actuating fluid in said chamber on said twofaces of said piston.
 13. A nozzle as claimed in claim 10, wherein saidvalve pin is removably connected to said actuator.
 14. The valve pin asclaimed in claim 1, wherein said thermocouple is positioned at leastpartially within said valve pin body.
 15. An injection molding machinecomprising: a manifold having a manifold melt channel for receiving amelt stream; a nozzle having a nozzle melt channel for receiving themelt stream from said manifold melt channel and delivering the meltstream to a mold cavity; and a valve pin slidable within the manifoldand nozzle melt channels, said valve pin having a valve pin body with athermocouple, wherein said valve pin thermocouple is positionable withinsaid manifold melt channel for measuring a temperature of the melttherein.
 16. The injection molding machine as claimed in claim 15,wherein said valve pin thermocouple is positionable within said nozzlemelt channel for measuring a temperature of the melt therein.
 17. Theinjection molding machine as claimed in claim 16, wherein the moldcavity receives melt from a plurality of mold gates.
 18. An injectionmolding machine comprising: a nozzle having a nozzle melt channel forreceiving a melt from a melt source and delivering the melt to a moldcavity via a mold gate; a valve pin slidable within the nozzle meltchannel; a first thermocouple with a sensing portion coupled proximate aforward end of said valve pin; and a second thermocouple with a sensingportion coupled to said valve pin and spaced from said sensing portionof said first thermocouple.
 19. The injection molding machine as claimedin claim 18, wherein the forward end of said valve pin is adapted to beseated in the mold gate and the sensing portion of the firstthermocouple measures a temperature of the melt proximate the mold gate.20. The injection molding machine as claimed in claim 19, wherein thesensing portion of the second thermocouple is positioned on a centralportion of said valve pin for measuring a temperature of the meltproximate a central portion of said nozzle melt channel.